Transition-transversion bias is not universal: a counter example from grasshopper pseudogenes.

Conversely, as expected for a protein-coding gene evolving under selective constraints, the substitutions attributed to the genuine mitochondrial lineage showed a highly significant codon position bias ( χ 2 = 12.72, df = 2, p = 0.0017), in which mutations at the third codon position were overrepresented (94 versus 74.5).

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